Levitation of one magnet above another against the force of gravity can be accomplished by positioning the two magnets with the polarity of the upper (levitated) magnet opposite that of the lower (supporting) magnet so that the like poles (north or south) of the two magnets confront one another. Such nearly frictionless supporting of one magnetic body by another holds great potential for technological and commercial applications and great appeal for recreational and entertainment applications. Unfortunately, such juxtapositions of magnets are inherently unstable and usually must be mechanically constrained against lateral and flipping movement if the magnetic vertical lifting force is to be effective or useful. Nevertheless, special methods and apparatus have been developed for achieving magnetic levitation that do not require mechanical constraints.
One approach is to use electromagnets or combinations of permanent magnets and electromagnets with sophisticated automatic control systems that rapidly alter or modify the magnetic fields so as to prevent the lateral and flipping movements. This is one technique that is applied, for example, in magnetically levitated (maglev) trains and spinning rotor molecular drag vacuum gauges. Another method allows one permanent magnet to float (levitate) in the magnetic field of another permanent magnet without the use of any external controls, electrical circuits or mechanical constraints. U.S. Pat. No. 5,404,062 and U.S. patent application Ser. No. 08/413,949 filed Mar. 30, 1995 disclose such a levitation system. This system, now being produced and sold under the registered trademark, LEVITRON.RTM., uses a flat lower magnet to magnetically support or levitate a smaller spinning magnet. The smaller magnet has an annular or ring shape with a non-magnetic spindle fitted into the central hole thereof, the combination thus resembling a toy top. The system is operated by first placing a sheet of nonmagnetic material such as a plastic sheet on the lower magnet. The top is pressed gently against the plastic sheet and is set spinning either manually or with a mechanical device. The plastic sheet, bearing the spinning top, is then manually lifted upwardly. When the top reaches a certain height above the lower magnet (usually about one to four inches), it rises off the plastic sheet and remains spinning stably in space, supported only by the force from the interacting magnetic fields of the two magnets. The top will continue to spin for several minutes, its rotational speed gradually decreasing due to air drag. When the speed falls below that required to maintain stability, the top flips over and falls to the lower magnet.
U.S. Pat. No. 4,382,245 to Harrigan discloses another simple magnetic levitation system which utilizes a dish-shaped lower magnet to magnetically support or levitate a magnetic top spinning coaxially above the lower magnet. The dish-shaped or concave surface of the lower magnet is said to produce radially inwardly directed lines of magnetization which, together with the gyroscopic effect of rotation of the magnetic top, provide stabilization of the levitation system. The Harrigan patent also discloses that the top may be rotated manually or by air jets or rotary or oscillating magnetic or electric fields.
In U.S. patent application Ser. No. 08/506,351 filed Jul. 24, 1995, the disclosure of which is incorporated herein by reference, there are disclosed a method of and an apparatus for extending the duration of levitation of a rotationally stabilized magnetic levitation device, such as that disclosed in U.S. Pat. No. 5,404,062 and the aforesaid U.S. patent application Ser. No. 08/413,949, from its normal duration of several minutes to durations of up to many hours, or essentially indefinitely. That is accomplished by a plurality of fluid streams, such as air, directed at the top, with a radial component and a component tangential to the periphery, of the spinning top. An annular manifold connected to the outlet of one or more small air pumps is used to maintain the top spinning. The manifold distributes the air to a number of slender tubes comprising a set of air jets. The manifold is supported in such a way that the jet outlets or nozzles are arrayed in a circle about the spinning top and in a horizontal plane at the levitating height of the top. The air nozzles are directed in the horizontal plane of the top and the air streams projected in this plane have both tangential and radial components relative to the periphery and spin axis of the top, respectively. The top periphery is preferably provided with reaction surfaces, such as vanes, protuberances, roughened surfaces or the like. Such surfaces react with the air streams coming from the air nozzles and transfer the linear momentum of the air streams to angular momentum of the top, thus maintaining the rotational velocity of the top against air drag.
In the aforesaid U.S. patent application Ser. No. 08/672,672 of which this application is a continuation-in-part, another method of and an apparatus for extending the duration of levitation of a rotationally stabilized magnetic levitation device, such as the levitated spinning top disclosed in U.S. Pat. No. 5,404,062 and U.S. patent application Ser. No. 08/413,949, are disclosed. According to that invention, a flat base magnet is magnetized such that the field lines of its magnetic field are substantially perpendicular to the flat surfaces of the base magnet as described in U.S. Pat. No. 5,404,062 and U.S. patent application Ser. No. 08/413,949. The magnet of the spinning top is magnetized such that the field lines of its main magnetic field are substantially parallel to the spin axis of the spinning top. In that combination, when the top is spun manually about a vertical axis over the base magnet at a rotational speed or spin rate of about 18-35 cycles per second (cps) or about 1080-2100 rpm, the spinning top will be levitated above the base magnet for several minutes, e.g., 2-5 minutes. As used herein, the terms "vertical" and "horizontal" are determined with reference to the local vertical at the spin axis of the top.
According to the invention of the aforesaid application Ser. No. 08/672,672, it is possible to increase the duration of levitation of the spinning top by locating a horizontal component of a magnetic field in the region of the spinning top and pulsing that magnetic field between a minimum and a maximum value at a selected repetition rate. The pulse repetition rate of the field varies from a relatively low pulse rate, e.g., on the order of about 15 pulses per second (pps), to a higher pulse rate, e.g., on the order of about 30 pps. A square wave pulse or haversine wave pulse are both effective in maintaining the top spinning although other pulses including negative or positive or alternating pulses, clipped sine waves, etc., will work.
The pulsed magnetic field is achieved by locating one or more conductive wire coils in a position with respect to the magnet of the spinning top so that when a pulsed dc voltage is applied to the coil a pulsed horizontal field is generated at the spinning top. The pulsed magnetic field is applied before or after the top is spun either manually or by any other means. The spinning top is subjected to the horizontal component of the pulsed magnetic field at a pulse repetition rate less than the spin rate. As the rotational speed or spin rate of the top decreases naturally because of drag, the top will couple to the pulsed magnetic field generated by the coil or coils at a spin rate of about 30 cps (1800 rpm) The spin rate is maintained at approximately 1.25 to 1.5 times the pulse rate.
The magnetic field which generates the horizontal field component at the spinning top is provided by a conductor wire wrapped about the base magnet with the axes of the windings oriented along any horizontal axis, or by a coil or coils disposed above or below the base magnet or in a central opening thereof or above the location of the spinning levitated top with the axis or axes of the field or fields generated thereby arranged along a horizontal axis or axes at any azimuthal angular orientation with respect to the local vertical.
As also described in the aforesaid U.S. Pat. No. 5,404,062 and U.S. patent application Ser. No. 08/413,949, adjustment of the weight of the spinning top is necessary to obtain the proper relationship of spinning top mass and the interacting magnetic fields of the base and top so that levitation of the top can be maintained for a reasonable period of time. The weight adjustment is accomplished by adding or removing washers of different weights to the top spindle and securing them in place with a rubber grommet or O-ring.